Recently, an attention has been paid to isothiocyanates having a substituent at the 5-position, for example, an isothiocyanate represented by the following formula, ##STR1## , wherein X.sub.1 and X.sub.2 each represent a halogen atom and R represents an alkyl group, as an intermediates used for production of thiazabicyclononane derivative or monothiourazole derivative. Such an isothiocyanate has conventionally been produced by a process represented by, for example, the following reaction formula. ##STR2## This process gives an excellent yield but has had problems in that the thiophosgene CSCl.sub.2 used is difficult to procure because of its high toxicity and transportation problem, making it difficult to carry out the process industrially.
For the conversion of aniline to isothiocyanate as aimed at in the above conventional process, there are known, for example, a process represented by the following reaction formula, ##STR3## which is described in "Shin Jikkenkagaku Koza 14 (phonetical translation), Syntheses and Reactions of Organic Compounds III", pp. 1504-1505, compiled by the Chemical Society of Japan and published by Maruzen Co., Ltd. on Feb. 20, 1978, and a process using a special base, i.e. 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), represented by the following reaction formula ##STR4## (in this process, the amine is an aliphatic amine, an alicyclic amine or an aromatic amine), which is described in Japanese Patent Application Kokai (Laid-Open) No. 33359/1988. Hence, it is considered to use these processes in producing the isothiocyanate represented by the above formula (1).
However, when the conventional process described in "Shin Jikkenkagaku Koza 14" is applied for producing an intended isothiocyanate from an aniline having a substituent at the 5-position, no reaction proceeds. And when the conventional process described in Japanese Patent Application Kokai (Laid-Open) No. 33359/1988 is applied for producing an intended isothiocyanate, the yield is as low as about 35% and the resulting isothiocyanate is converted to an ultimate product via further several steps; thus, this process is not suitable, either, for industrial application.
The present invention has been made in order to solve the above-mentioned problems of the prior art and provide a dithiocarbamic acid salt which can be converted, at a very high yield, to an isothiocyanate suitable for use as an intermediate for production of thiazabicyclononane derivative or monothiourazole derivative, and a process capable of producing said dithiocarbamic acid salt at a high yield without using any compound having toxicity problem.
The present invention has also been made in order to provide a process for producing the above isothiocyanate using said dithiocarbamic acid salt.